I created a sensor board that could monitor the air quality with a high degree of accuracy and sense many different pollutants and gasses, this is still a work in progress but ill share what I have already created.
Specification
- CO2 400-2000ppm (+-50ppm + 5%)
- humidity 0-100% (+-3%)
- Pressure: 300-1100 hPa (+-0.25%)
- Particle detection: 0.3~1.0; 1.0~2.5; 2.5~10 µm (0-500µg, +-2%)
- Temperature: 0.1C
- CO: 20-2000ppm (accuracy: TBD)
Using the MICS6814 a whole range of other gasses can also be detected, this sensor has 3 sensing elements that combine some of the gasses, so this is not useful to identify a specific gas or get an accurate ppm value, this mainly indicated one of more of these gasses are present and maybe get a rough idea of the concentration.
- Carbon monoxide CO 1 – 1000ppm / CO
- Nitrogen dioxide NO2 0.05 – 10ppm / NO2
- Ethanol C2H5OH 10 – 500ppm / CO – NH3
- Hydrogen H2 1 – 1000ppm / NH3 – CO – NO2
- Ammonia NH3 1 – 500ppm / CO – NH3
- Methane CH4 >1000ppm / CO – NH3
- Propane C3H8 >1000ppm / CO – NH3
- Iso-butane C4H10 >1000ppm / CO – NH3
Hardware
CO2 SCD40
One of the most important air quality metrics is the amount of CO2 in the air, therefore I chose a more expensive but acurate sensor
Advantages:
- Absolute measurment and no need to calibrate (factory calibration)
- very small package
- I2C communication
- Good CO2 accuracy (+-50ppm +- 5%)
- High range (400-2000ppm)
Disadvantages:
- High Cost (€15-30 depending on source)
- high current peaks (205mA)
- Other onboard sensors not acurate (temperature and humidity)
- Self heating
Particle matter concentration sensor
An important air quality metric is the amount of dust or small particle matter in the air.
High levels are a big health hazzard.
Soldering or other exhaust fumes from cars for example can emit large amounts of these small harmfull particles, in small rooms these level can rise very high wihout proper ventilation or filtering.
These are the air quality levels set for Europe, these vary from region to region.
I use the PMSA003 sensor the detect particles from 0.3 -> 10µm devided into 3 groups.
0.3~1.0µm
1.0~2.5µm
2.5~10µm
I chose the PMSA003 mainly because of its small size while still being able to detect a large range of particle sizes and high concentrations.
Full datasheet:
MICS-6814 gas sensor
The MICS-6814 sensor is used to measure a large range of different gasses by using 3 sensing elements.
MQ7 CO sensor
The MQ7 is a CO sensor used to get an idea CO concentration in the air.
Because it is not a validated sensor it can not be relied upon for life saving warnings.
But it is good enough for some experimentation and detection.
ADS1115 ADC
WIP
BME680 humidity and presure sensor
WIP
TMP117 0.1c temperature sensor
The TMP117 is a very accurate temperature sensor with a factory calibration of 0.1c.
Because of that great care is needed to not influence the sensor with the heat of nearby components.
That’s why this PCB has the sensor located at the edge on the far side of the airflow.
It also has a cutout around it to minimize heat transfer trough the PCB and minimize the thermal energy.
DS18B20 0.5c temperature sensor
The DS18B20 is a simple and cheap temperature sensor.
Used on this board if the TMP117 is not needed for the accuracy and save on cost.